Shift of optimum angle after concentric-only exercise performed at long vs. short muscle length

Aim of this study was to evaluate shift of optimum angle in hamstrings and quadriceps after single resistance exercise session performed at different muscle lengths. Thirteen healthy sport students volunteered for this study. The intervention consisted of ten sets × ten maximal concentric-only knee flexions or extensions exercised at long muscle length in hamstrings and short muscle length in quadriceps. Total work for each set was recorded and analyzed. Before and immediately after the exercise session isometric maximal voluntary contraction (MVC) was recorded both for hamstrings and quadriceps at 20°, 30°, 40°, 50°, 60°, 70° and 80° of knee extension. Compared to the first set, total work significantly decreased starting from the second set in hamstrings and from the fourth set in quadriceps. Immediately after exercise, MVC was significantly (p <0.05) lower than baseline in all conditions. The optimum angle shifted towards longer muscle in hamstrings (from 50° to 20°) but not in quadriceps (pre and post = 70°). Our outcomes showed that concentric-only resistance exercise performed at long (hamstrings) but not at short (quadriceps) muscle length induced shift of peak joint torque angle towards longer muscle. However, different rate of fatigability between hamstrings and quadriceps could have influenced such shift.